Draytek to Watchguard Site to site VPN behind a BT Home Hub 5 at one end?

I have a customer who has two physical buildings (HQ and satellite office)

HQ have a dedicated BT leased line at 100mbps. They have a WatchGuard firewall, and the external interface is configured with a static public IP.

The Satellite office HAD a BT ADSL line with static IP. This was connected to a DrayTek 2830n router. This router has Wi-Fi VLANs enabled for staff and customers,

I also HAD 2 branch office (LAN-to-LAN, Site-to-site - whatever you want to call them) VPNs working (for staff networking and for VoIP phones).

However, the customer has "upgraded" the Satellite office line to BT Infinity. A Home Hub 5 was supplied by BT and now sits in the middle of what was working before. The DrayTek 2830n is now plugged in to the BT Home Hub 5, and of course the VPNs no longer work.

In the Home Hub, I have tried using Port forwarding of ports 50, 51, 500 and 1723 to the DrayTek, and I have tried adding the DrayTek as a DMZ, but I just can't get the VPNs to work.

Is there a way of doing this without ditching the current Home Hub and DrayTek 2830 in favour of a DrayTek 2860 VDSL router?
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Chris MillardAsked:
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JohnBusiness Consultant (Owner)Commented:
A Home Hub 5 was supplied by BT and now sits in the middle of what was working before  <-- This might introduce a double NAT. Can you enable NAT Traversal on the VPN to see if that works?

Did the new device change the external IP of the office?
Chris MillardAuthor Commented:
The external IP at the office remains the same. I'm not sure about enabling NAT Traversal. I'll take a look!
Chris MillardAuthor Commented:
After some further investigation, the Home Hub 5 will NOT work in this scenario. I have been informed that the BT device would need to be in modem only mode (which it does not do).

From BT's perspective, they suggested installing a BT OpenReach modem (which I know would work - but is an expensive option), so I have removed the HH5 altogether and at the advice of DrayTek, have installed a Vigor 130 instead.

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Chris MillardAuthor Commented:
Problem is with the HomeHub 5.
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